The ultimate aim in the prevention of transplant rejection is the development of more specific therapies thus eliminating the potentially serious complications associated with current immunosuppressive drugs. The interaction between the TCR and a complementary MHC + peptide complex is central to the immune response to alloantigens. Since MHC peptides are known to be abundantly bound to MHC molecules it has been proposed that they may play an immunoregulatory role in vivo. We have demonstrated that nonpolymorphic class II MHC peptides inhibit T cell proliferation, cell mediated cytotoxicity and cytokine production. The aim of our research proposal is to investigate the mechanism of action mediating the immunomodulatory effects of these peptides and to determine their role in preventing allograft rejection. We will identify peptide binding proteins by means of immunoprecipitation and Western blot analysis, and perform studies to determine whether variation in the sequence of the peptides alters their binding affinity and function. There is now substantial evidence that T cell activation is not an "all or none" event, but rather the TCR can recognize subtle changes in the peptide ligand presented to it resulting in a differential T cell response. This altered T cell response may result in a state of of partial activation or "immune deviation" (Th1/Th2). Induction of energy will be assessed by studying the effect of the peptides on T cell activation, in particular, intracellular calcium flux and cell surface expression of specific markers of T cell activation and reversal of unresponsiveness by exogenous cytokines. In addition, the induction of apoptosis in hyporesponsive cells will be assessed. The association of inhibition of T cell function by non-polymorphic class II MHC peptides with a state of "immune deviation" will be determined by examining patterns of cytokine production using semi-quantitative RT-PCR and ELISA. The in vivo application of these peptides will first be tested by examining their ability to inhibit a specific delayed type hypersensitivity response initiated by immunization with an immunogenic MHC allopeptide or alloantigen-specific T cell clones. We will evaluate the ability of these peptides to prolong allograft survival in an in vivo model of acute renal allograft rejection. Allografts will be studied by RT-PCR and detailed immunohistology to examine intragraft cytokine expression and growth factors. The long term goal is to determine the potential role in the of these